This invention relates to digital magnetic recording, and more particularly to a magnetic recording disk drive where data is written while the magnetic recording layer is at an elevated temperature.
Magnetic recording disk drives store digital information by using a miniaturized thin film inductive write head. The write head is patterned on the trailing face or surface of a head carrier, typically a slider that also has an air-bearing surface (ABS) to allow the slider to ride on a thin film of air above the surface of the rotating disk. The write head is an inductive head with a thin film electrical coil located between the pole pieces of a magnetic yoke. When write current is applied to the coil, the tips of the pole pieces provide a localized magnetic field across a gap that magnetizes regions on the recording layer on the disk into one of two distinct magnetic states that represent the recorded data bits.
The magnetic material for use as the recording layer on the disk is chosen to have sufficient coercivity such that the magnetized data bits are written precisely and retain their magnetization state until written over by new data bits. The data bits are written in a sequence of magnetization states to store binary information in the drive and the recorded information is read back with a use of a read head that senses the stray magnetic fields generated from the recorded data bits. Magnetoresistive (MR) read heads include those based on anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), such as the spin-valve type of GMR head, and the more recently described magnetic tunnel junction (MTJ) effect. Both the write and read heads are kept in close proximity to the disk surface by the slider""s ABS, which is designed so that the slider xe2x80x9cfliesxe2x80x9d over the disk surface as the disk rotates beneath the slider.
As the recording bit size decreases to increase the data density on the disk, a problem arises with the conventional thin film inductive write head and writing process that is referred to as the xe2x80x9csuperparamagneticxe2x80x9d effect. The areal data density (the number of bits that can be recorded on a unit surface area of the disk) of magnetic disk drives is approaching the point where the data bits are so small they can be demagnetized simply from thermal agitation within the magnetized bit (the so called the xe2x80x9csuperparamagneticxe2x80x9d effect). The conventional approach to circumventing this problem is to increase the magnetic anisotropy and coercivity of the magnetic material in the recording layer on the disk to improve the thermal stability. However, this requires that the write head be made with a material with high saturation moment to increase the write field of the head so the head can write on the high coercivity media. Based on the properties of known materials, the ultimate write field of the head can only be increased by about 30%, thus severely limiting future data density growth. In addition, the increased data rate required at higher areal density requires that the magnetic properties of the materials used in the write head have to be optimized, which is very difficult to achieve if the materials suitable for use are limited to only those that have a very high saturation moment.
Since it is known that the coercivity of the magnetic media (i.e., the magnetic recording layer on the disk) is temperature dependent, one proposed solution is xe2x80x9cthermally assistedxe2x80x9d magnetic recording (TAMR), wherein the magnetic material in the media is heated locally to near or above its Curie temperature during writing so that the coercivity is low enough for writing to occur, but high enough for thermal stability of the recorded bits at ambient temperature. Several approaches to TAMR have been proposed, including use of a laser beam or ultraviolet lamp to do the localized heating, as described in IBM Technical Disclosure Bulletin, Vol. 40, No. 10, October 1997, pp. 65-66, and IBM""s U.S. Pat. No. 5,583,727. In these approaches, the heating area is typically wider than the data bit so that the data bit dimension is still determined by the size of the write head.
One of the problems still to be addressed in TAMR is the design of a write head that co-locates the heat and the magnetic write field to the same spot on the magnetic layer of the media, preferably to a region no larger than the size of the data bit to be recorded. A write head for use in a magneto-optic (MO) or TAMR system is described in U.S. Pat. No. 5,986,978, wherein a special optical channel is fabricated adjacent to the pole or within the gap of the inductive write head for thermally assisted writing of the MO or magnetic media by directing laser light or heat down the channel. IBM""s previously cited application Ser. No. 09/608,848 describes a TAMR write head that uses a conventional thin film inductive write head and an electrically separated resistive heater located in the write gap between the pole tips of the inductive write head. The resistive heater directs heat to a region on the magnetic layer of the disk and the pole tips of the inductive write head direct the magnetic write field to the heated region. These TAMR head designs that use a separate heating element isolated from the inductive write coil require complex fabrication processes and/or electrical wiring layouts.
What is needed is a TAMR write head that co-locates heat and the magnetic write field and that is easier to fabricate and implement in a TAMR system than prior TAMR write heads.
The invention is a thermally-assisted write head to simultaneously generate heat and a magnetic write field to the magnetic recording layer on the disk, and a TAMR disk drive that uses the write head. The write head is located on the trailing face of a head carrier and comprises a single turn coil, part of which is a current strip having an edge located at the disk-facing surface of the head carrier. When write current is passed through the current strip heat is generated at the edge of the strip and a magnetic field is induced at the disk surface. The strip edge has a predetermined width that substantially corresponds to the desired track width of the data bits. Because both heat and the magnetic write field are generated by the same element, the heat gradient and the magnetic write field gradient are co-located on the spot on the recording layer where the data bit is written. In a second embodiment a magnetic yoke surrounds the single turn coil with the current strip located in the write gap between the pole tips of the yoke, so that current through the strip also induces a magnetic write field across the pole tips. In a third embodiment the single turn coil is the primary turn of a multi-turn coil, with the secondary coil turns located in the yoke but away from the current strip and the pole tips.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.